This application is in response to PA-12-113, Research on the Health of LGBTI Populations, which encourages researchers to investigate new questions related to LGBTI health with high priority placed on research on interventions for [LGBTI] individuals. Survivorship of prostate cancer (PCa) is one such area. Across the lifespan, 1-in-6 gay and bisexual men (GBM) and 1-in-3 male couples will be diagnosed with PCa, making PCa the most common cancer affecting GBM. Yet, almost no research has examined the effects of PCa treatment on GBM's sexual functioning. Sexual dysfunction is the major sequela of PCa treatment, which is deeply distressing in itself, and negatively impacts quality of life post-treatment, resulting in serious negative mental health outcomes. Recent studies indicate sexual outcomes of PCa treatment are significantly worse for GBM than heterosexual men. Physiological differences between anal sex and vaginal sex likely explain, at least in part, this health disparity. Tailored treatment needs to be developed, but is almost entirely unexplored. Missing is research to evaluate the effects of PCa treatment on GBM sexual functioning, research on rehabilitation outcomes, and research to guide development of new treatments tailored to GBM and sex between men. The long-term objective of this research is to develop the first evidence-based PCa rehabilitation curriculum tailored for GBM. As a first step, in this R21 we will conduct the formative research needed to estimate the extent of poor outcomes, confirm need, and assess acceptability and feasibility. There are three specific aims. In Aim 1, we will investigate, in-depth, the experience of PCa treatment on the sexual lives of GBM, their partners, and their relationships. We will conduct a semi-structured, chat or phone interview study of up to 48 GBM PCa patients, partners, and couples, nationally. In Aim 2, we will refine definitions and develop the measures needed to assess sexual dysfunction in GBM. In Aim 3, we will conduct an online quantitative survey of 220 GBM with PCa, which will a) quantify sexual challenges post-treatment, b) assess needs and priorities for rehabilitation, c) develop a new scale to measure sexual functioning in GBM and d) assess the acceptability and feasibility of a new rehabilitation curriculum for GBM with PCa.